1. Field of the Invention
The present invention relates to tank venting valves for relieving the internal pressure in tanks at a predetermined pressure. More specifically the invention is concerned with whether a venting valve has opened and how much.
2. Related Art
There are several types of pressure relief valves for atmospheric or low pressure storage tanks. One of the basic designs is known as a "weight loaded tank vent". The design utilizes a weighted cover over a nozzle. The cover, also known as a pallet, forms a barrier to the nozzle opening. The weight of the pallet determines at what pressure the pallet will lift open to relieve pressure in the tank. The opening pressure is known as the "set pressure". The set pressure can easily be determined by dividing the weight of the pallet assembly by the open area of the nozzle. If a higher set pressure is desired more weight is added to the pallet.
Other types of pressure relieving devices include a spring loaded tank vent and a pilot operated tank vent. The spring loaded type is used for set pressures above that which is practical for weight loaded operation due to either a high set pressure where there is not enough room for the weights on the pallet, or where the size of the vent nozzle dictates a large weight on the pallet.
Pilot operated tank vents utilize the tank pressure acting on an area larger than the nozzle area to create a higher downward force to hold down a pallet or seat plate against the tank pressure. The set pressure is adjustable by means of a spring in the pilot.
Any of the three types may be vented to the atmosphere or piped into headers for vapor recovery or burning. Generally these valves open, make an emission and close without any record and can present a source of atmospheric contamination.
It is an advantage that the present device requires no electrical or auxiliary mechanical power to operate and will not interfere with the breather vents function or relief capacities. It is a feature that the present device provides a visible display that remains after the vent is closed to show that it was open and provide an indication of the extent of the opening. These and other features and advantages will become apparent from the following descriptions.